The present invention is curable organopolysiloxane compositions which cure by the addition reaction of silicon-bonded lower alkenyl radicals with silicon-bonded hydrogen atoms and which exhibits improved adhesion to a variety of substrates. The compositions comprise an adhesion promoting mixture comprising an epoxy-functional compound, a compound having at least one hydroxy group and in the same molecule at least one substituent selected from a group consisting of silicon hydride, alkenyl, and acryl, and an aluminum compound or zirconium compound. Compression set of the cured organopolysiloxane compositions is generally not significantly effected by the adhesion promoting mixture.
Organopolysiloxane compositions curable by a platinum catalyzed addition reaction of an organohydrogensiloxane to an organopolysiloxane containing ethylenically unsaturated hydrocarbon radicals have been used in numerous fields of industry because they do not generate by-products during curing, can be cured by heating at relatively low temperatures for short periods of time, have excellent flame retardancy, have excellent elastomeric properties, and have the ability to function as electrical insulators.
However, because addition-curable organopolysiloxane compositions do not adhere well to substrates with which they are in contact during curing, the surface of the substrate must be preliminarily treated with a primer if secure contact is to be maintained. This is disadvantageous from the standpoint of productivity, labor, and cost. As a consequence, numerous techniques have been proposed for imparting adhesion ability to such organopolysiloxane compositions by, among other means, the blending of particular types of silanes and polysiloxanes into such compositions.
Schulz, U.S. Pat. No. 4,087,585, describes a self-adhering silicone rubber composition which employs an adhesion promoting mixture comprising a polysiloxane having at least one silicon-bonded vinyl radical and at least one silicon-bonded hydroxyl radical and an epoxy-containing alkoxysilane.
Matsumoto et al., JP (Kokai) 60-101146, describe an adhesive polyorganosiloxane composition which employs an epoxy compound as an adhesion promotor and an organic aluminum compound.
Plueddemann, U.S. Pat. No. 4,659,851, describes a class of silane compounds which can cohesively bond organopolysiloxane elastomers and resins to organic and inorganic substrates. Included in the this class of compounds are compounds comprising at least one hydroxy group and in the same molecule at least one substituent selected from a group consisting of silicon hydride, alkenyl, and acryl.
Morita et al., U.S. Pat. No. 4,742,103, teach the adhesion of organopolysiloxane compositions curable by a platinum catalyzed hydrosilation reaction to various substrates is improved by the presence in the compositions of an organosilicon compound containing an ethylenically unsaturated group and at least one alkoxy group and at least one member from a class of compounds of aluminum or zirconium.
Osamu et al., EPO Application No. 0-497-349 A2, teaches organosiloxane compositions containing an adhesion promoter consisting essentially of a first organosilicon compound containing both silicon-bonded unsaturated and silicon-bonded alkoxy groups, a second organosilicon compound containing both silicon-bond epoxy and silicon bonded alkoxy groups, and an aluminum compound or zirconium compound.